The present invention relates to a system for monitoring the operating condition of implanted electronic prosthetic devices such as cardiac pacemakers.
Periodic assessment of the operation of implanted electronic prosthetic devices such as cardiac pacers is desirable to ensure optimum performance and to guard against prolonged loss of proper functioning. Although many successful monitoring techniques have been in use, including the transmission of monitored data by telephone to fully equipped data centers, with the advent of longer implant lifetime through improved power sources, rechargeability, and the use of hermetic enclosures, the development of further monitoring methods is called for to adapt to the new devices. For example, modulation of the stimuli rate to monitor battery voltage in rechargeable cardiac pacers is technically undesirable because of the wider voltage variable encountered from the repeated recharging activity. Furthermore, it is generally desirable to employ voltage stable pacing oscillators so that pacing rate deviations can be utilized to determine impending component failure that would dictate emergency replacement. The data bandwidth employing pacemaker rate as the only data carrier also precludes the telemetry of other higher frequency pacemaker parameters. On the other hand, common RF telemetry techniques are not compatible with the growing use of hermetically sealed metallic enclosures. Additionally, means for non-disruptive or passive monitoring of ventricular controlled pacemakers is desirable. Presently adaptive pacemakers have to be forced to operate in a competitive fixed rate mode for monitoring, which is psychologically undesirable for some patients.
The present invention accordingly provides a pacemaker telemetry system incorporating an improved low power, low-voltage, frequency-voltage sensitive pulse generator for supplying pulse-interval-modulation telemetry of implant battery voltage. The oscillator is independent of the pacing function and allows for passive non-disruptive monitoring of the battery voltage and other pacemaker parameters. The system is also capable of monitoring dynamically separable functions, such as the pacing rate and refractory-delay-time of demand pacers and is compatible in frequency with electromagnetic transmission through metallic enclosures and with direct telecommunications.